Hmm, difficult to find ...

Would this one suit from eBay US - http://www.ebay.co.uk/itm/Apple-PowerBook-G4-A1025-Series-PRAM-CMOS-BIOS-Battery-With-Cable-820-1343-A-/151147143077?pt=LH_DefaultDomain_0&hash=item2331125fa5 - seems to be $10 to buy and about $9 to ship to NZ,

or this one from France - http://www.ebay.co.uk/itm/Pile-Bios-EFI-Rtc-Batterie-CMOS-Apple-PowerBook-G4-Titanium-15-820-1343-A-/261278119601?pt=FR_GH_Informatique_Composants_Alimentation_PC&hash=item3cd563b6b1#shpCntId - they seem to be the only ones available worldwide from eBay.

If you get desperate I could buy the UK one for you and send it out.

Cheers

Hugh